1. Field
The invention is in the field of explosives, especially those using nitrate salt oxidizers, and specifically ammonium nitrate-fuel oil explosives (ANFO).
2. State of the Art
Explosives and blasting agents are an important part of the mining industry. It is estimated that over three billion pounds of explosives are used each year in the mining industry in the United States alone. The most commonly used explosive is a mixture of about 94% ammonium nitrate (AN) and about 6% fuel oil (OF), commonly referred to as ANFO. It is sold in the form of dry, loose particles called "prills" generally marketed in bags or in bulk.
Explosive power is measured in terms of weight strength and bulk strength. The term "weight strength", usually expressed in kilocalories per gram, is used to compare explosives which employ nitrate salt oxidizers with ANFO explosives, the standard for the industry. The value of the weight strength for ANFO is frequently assumed to be 1.0 kcal/gm. Bulk strength, a function of the density of the explosive, is used to compare the explosive power of two products on a bulk or volume basis. The higher the volume density, the higher the bulk strength. Its unit of measure is kilocalories per cubic centimeter, abbreviated kcal/cc.
ANFO is relatively inexpensive and widely used, however, its low volume density (about 0.8 gm/cc) limits the amount of useful energy that can be obtained per charge. Efforts to increase the density and therefore the bulk strength of ANFO have included methods using finely ground ammonium nitrate as opposed to nitrate prill particles and the use of high density metallic fuel additives such as aluminum or ferrosilicon.
In addition, ANFO is desensitized by water, precluding its use in water-filled boreholes. In efforts to provide a waterproof ANFO, many water-in-oil and oil-in-water emulsion products have been described in numerous patents. Attempts have also been made to waterproof ANFO by using thickeners and cross-linkers; for example, Sheeran, U.S. Pat. No. 4,933,029 and Stromquist and Wathen, U.S. Pat. No. 4,693,763.
Not only have there been numerous attempts to increase the explosive power and waterproof properties of ANFO explosives, other attempts have been made to provide for easier handling, transporting and loading of the product. These efforts have met with limited success.
There remains a need in the industry for inexpensive, easily manufactured explosives having equal or increased explosive power when compared to ANFO which are easily and safely transported, stored, and loaded; are water-resistant; and which have negligible impact on the environment.